Why do we love knit fabric so? Because of its s-t-r-e-t-c-h. That said, finding the right knit fabric for a sewing project can stretch anyone's patience. Here's how to find what you need, every time.
Know the stretch direction
You might think all knits stretch every which way, but that's not the case. Generally speaking, knits offer either two-way or four-way stretch.
Two-way stretch knits stretch in one direction — typically crosswise, from one selvedge edge to the other. Think of cotton interlock or the knit fabric most T-shirt are made of.
These fabrics are certainly comfy but don't provide the super stretchiness you want in leggings, say, or active wear.
Two-way stretch knits also don't have quite the same recovery as four-way stretch knits, meaning they don't snap back to the original shape when released. Over time your clothes might begin to droop, which is just as depressing as it sounds.
Four-way stretch knits can stretch in both directions: crosswise (from selvedge to selvedge) and lengthwise. That fabric can move with you in all directions. Think of two-way stretch knit as stretching right and left only (thus two-way) and four-way stretch knits as stretching right and left plus up and down (four-way).
When shopping for knit fabrics, do some tugging. You'll be able to tell quite quickly what the fabric can do.
Find out the stretch capacity
Not all knit fabrics are equal. Some have a lot of stretch, others not so much.
Here's an example of tugging on the fabric to gauge its stretch potential. See how far the green pin moves when the fabric is pulled?! This fabric stretched from 4" to 6", so it has 50 percent stretch. A fabric that stretches from 4 inches to 8 inches has 100 percent stretch.
Think about how the how the fabric will behave IRL
Activewear, form-fitting T-shirts, underwear and shapewear should stretch to fit your body. With the right fabrics, you're looking good. With the wrong ones, you're back to the sewing machine.
Consider the striped fabric above, a cotton knit with the stripes running lengthwise (which is actually not that common). If this fabric were used in a garment with negative ease, it would stretch out, as your see on the right. The stripes stretch, the color becomes lighter and you can see the white background.
This can happen when there's a print on the surface of the knit fabric. It can also happen when fabrics with a high Lycra content are stretched — that's when you get a bit of shine or transparency, which is definitely not the look you want in your yoga pants!
Watch out for novelty fabrics
Some knits try extra hard to be pretty. The pink knit shown above is a cotton interlock with two-way stretch, with small sequins stitched on top of the fabric.
Be aware that embellishments attached with regular machine stitching reduce the stretch factor. This fabric would still work for a loose-fitting T-shirt with a wide neckline, but might be too saggy for a blouse that relies on negative ease.
Match the stretch to the pattern
Most sewing patterns tell you the amount of stretch you'll need for the garment to fit well and sew up well. If you've ever sewn with a knit that wasn't stretchy enough, you know that it's difficult to get curves to match or to apply pieces smoothly. Avoid that #sewingfail.
On the pattern above, the black bar lets you check the stretch of the fabric: You fold over crosswise a 4-inch section, align it with the edge of the black bar and then pull it to the second arrow. If the fabric reaches that point, it's a stretch success.
Also take note of the suggested fabrics listed on your pattern. If a pattern indicates a jersey, a knit such as ponte that has less stretch likely won't work.